The present invention relates to anesthesia systems used to provide an anesthetic agent to a patient undergoing an operation.
In general, anesthesia systems are utilized in operating rooms and comprise various equipment necessary to anesthetize the patient and maintain the patient in that state until the operation is completed and it is possible to terminate the introduction of the anesthetic agent.
Such systems comprise various pressure regulators, flow control devices, gas mixing devices and vaporizers to vaporize a volatile liquid anesthetic and to introduce the anesthetic laden gases into the patient. The patient is connected to the system by means of a face mask or other device and which interfaces with the anesthesia system via a patient circuit that may typically have an inspiratory limb through which the gases are introduced into the patient and an expiratory limb that conveys the exhaled gases from the patient.
In one typical anesthesia system, the overall flow of gases to and from the patient may be in a generally closed circuit, commonly referred to as the circle system, that is, the patient is connected to a substantially closed volume supply of gases and rebreathes certain of those exhaled gases supplemented by fresh gas.
As the driving force to the circle breathing circuit, and, of course, to the patient, a ventilator is used and which basically breathes for the patient since the patient is under anesthesia and is unable to carry out the normal spontaneous breathing functions. The ventilator, therefore, provides a quantity of the gas containing a predetermined metered quantity of the anesthetic agent along with other gases such as nitrous oxide and, of course, a life sustaining percentage of oxygen.
That gas containing the anesthetic may typically be delivered through an intermediate mechanism such as a bellows. In such case, the driving gas from the ventilator does not contain the anesthetic agent but is used to simply power the bellows to collapse that bellows to deliver the aforementioned anesthetic containing gas from the bellows to the patient. Instead of drive gas, other driving means such as an electromechanical or mechanical means are also used.
In any of the aforedescribed systems, the anesthetic laden gas is delivered to the inspiratory limb of the circle patient breathing circuit and is introduced into the patient to provide anesthesia to that patient. That anesthetic gas to the inspiratory limb is provided by a source of gases, including fresh gas, oxygen and generally nitrous oxide, that is mixed to a predetermined mixture in a gas mixer and the mixed gases are then passed through an agent vaporizer where the anesthetic agent is introduced into those gases.
In the expiratory limb of the circle patient breathing circuit, as the patient exhales, the exhalation gases pass through the expiratory limb where they are recirculated back to the inspiratory limb where they are again inhaled by the patient. In this manner, the system is closed and which allows the optimum use of the rather expensive anesthetic agent. If the fresh gas added to the circuit exceeds the net of gases taken up by the patient or leaked from the circuit, the excess gases are popped off via a pop-off valve.
In the use of such anesthesia machines, it is important to have various safety features to ensure that the system is operating properly and, in the event there is some fault, that there is a prompt recognition of that fault and an immediate means to override the fault condition or faulty component to insure the safety of the patient.
One such fault can occur in the gas mixer, that is, the mixer that combines oxygen and other carrier gases such as nitrous oxide and air to provide the fresh gas that is added to the patient breathing circuit during the normal course of anesthesia. Potential faults in the mixing system include a loss of one or more of the added gases, a failure in the mixing system, failure of a flow sensor and the like. In general, such mixers are controlled by a central processing unit that senses the various critical flows and establishes the conditions to make those flows the same as inputted by the clinician or determined automatically by the machine.
In the case of such failure or fault in the mixing or supply system of the fresh gas to the patient breathing circuit, it is important that some alternate measure be provided to the clinician as well as sufficiently notifying the clinician of the occurrence of the fault condition. As an advantage, the alternate measure can provide some manual control to the clinician so that not only is the fault condition recognized, but the clinician can continue the application of oxygen manually to continue the particular operation until the patient can safely be taken off anesthesia. Obviously, in the mixing and supply portion of the anesthesia machine, it is paramount that the patient continue to receive the life supporting amount of oxygen until the fault has been corrected or the operation has been safely terminated and the patient taken off the faulty anesthesia machine.